The ability of water soluble polymers, with polar functionality, to hydrogen bond with cellulose fibers makes them suitable candidates for the paper industry. Use of functional polymers has shown improvement in paper making processes with regard to paper strength, drainage, retention and several other properties. Several patents and research articles discuss the use of functional polymers as a paper making additive. Functional polymers that are added as strength additives at the wet-end of the paper machine, especially in paper made from recycled fibers, include amphoteric acrylamide based polymers and coacervate technology. An example of the former is described in U.S. Pat. No. 5,698,627, issued to Oguni, which teaches the synthesis of acrylamide based amphoteric copolymers that improve freeness, retention, and dry strength of recycled corrugated base paper. An example of coacervate technology is described in U.S. Pat. No. 6,294,645. This wet-end dry strength system is comprised of a low charge polyamidoamine-epichlorohydrin and an anionic polyacrylamide, added sequentially to pulp slurry.
Polymers with amine functionality, such as vinylamine based polymers derived from N-vinylformamide (VFA), offers a material with distinctive properties. The pendant primary amine functionality generated on VFA hydrolysis makes these polymers highly cationic in nature. U.S. Pat. No. 2,721,140 discloses use of polyvinylamine as an additive to make papers having high wet strength, while U.S. Pat. No. 5,961,782 discloses the use of polyvinylamine to make crosslinked creping adhesive formulations.
U.S. Pat. No. 4,421,602 discloses a partially hydrolyzed, water-soluble polymer of N-vinylformamide that contains N-vinylformamide units and vinylamine units. It also discloses use of polyvinylamine and a 50% hydrolyzed polyvinylformamide to increase flocculation efficiencies, fines retention, and the drainage rate of pulp fiber in papermaking processes, while U.S. Pat. No. 6,159,340 discloses the use of such polymers as dry and wet strength additives in paper and paperboard production. U.S. Pat. No. 6,616,807 and U.S. Pat. No. 6,797,785 disclose use of polyvinylamines as drainage aids, flocculants, and retention aids in the paper making. As used herein vinylamine-containing polymer and polyvinylamine are used interchangeably.
Similarly copolymers of N-vinylformamide with functional vinyl monomers are also well studied. U.S. Pat. No. 4,774,285 discloses that N-vinylformamide monomer may be copolymerized with an additional vinyl monomer, e.g., vinyl acetate, and subsequently hydrolyzed to produce a water-soluble copolymer of vinylamine and vinyl alcohol, which may be used as wet and dry strength additives for papermaking. U.S. Pat. No. 5,630,907 discloses copolymer compositions containing vinyl amine and acrylic acid units, as well as their applications. U.S. Pat. No. 6,797,785 discloses copolymers containing vinylamine units in combination with either diallyldimethylammonium (chloride) (DADMAC) or acrylamide units via reverse emulsion polymerization, and their use as flocculants and coagulants in papermaking. EP 0251182 discloses copolymers containing vinylamine and acrylonitrile units for use in papermaking as drainage aids, retention aids, as well as wet end additives for increasing the dry strength of paper products.
Hofmann degradation of polyacrylamides is another approach to introduce primary amine functionality to polymers. Tanaka and Ödberg, in J. Polym. Sci. Part A: Polymer Chemistry 1989, (27) 4329-4339, describes a method of preparing polyvinylamine via a Hofmann reaction of polyacrylamide. U.S. Pat. No. 5,039,757 discloses manufacturing of cationic polyacrylamide by Hofmann degradation process using polyacrylamides and its copolymers. US Patent Application No. 2010/186,914 A1 and US Patent Application No. 2010/326,614 A1 disclose use of branched acrylamide copolymers and its subsequent Hofmann degradation to introduce primary amine functionality. However, use of hypohalogenite under alkaline conditions also results in hydrolysis of acrylamide functionality, and polymer degradation. Further purification of the polymer to remove residual hypohalogenite makes this approach expensive.
Modification of vinylamine based polymers is another approach to introduce additional functionality to the polymer and alter its physical properties. U.S. Pat. No. 8,604,134 discloses modification of polyvinylamine with different functional groups and its application as paper making additive. U.S. Pat. No. 7,902,312 discloses Michael adduct of polyvinyl amine with α,β-unsaturated alkyl carbonyl compounds and its subsequent use as an additive for paper making system. U.S. Pat. No. 5,994,449 discloses the use of vinylamine-vinyl alcohol copolymer functionalized with epichlorohydrin and its mixture with polyaminoamide as creping adhesive for paper application.
Graft copolymers of vinylamine based polymers is disclosed in U.S. Pat. No. 5,753,759. The disadvantage of this technology is that the pH and temperature conditions employed for graft polymer synthesis promotes side reactions leading to an unstable product and/or the unwanted Michael addition reaction of the grafting monomer on vinylamine base polymer, and/or product with very limited shelf life.
US patent application publication 2011/0155339 teaches a process for enhancing dry strength of paper by treatment with vinylamine-containing polymers and acrylamide-containing polymers. US 2011/0155339 describes a single-product blend that can react in aqueous solutions with primary amine groups in the vinylamine-containing polymer to form amide groups which may form a gelled or prohibitively high viscosity product which causes issues in papermaking.
The present invention relates to a process of graft polymerization of vinyl monomer based on a functionalized vinylamine-containing polymer and compositions thereof. Such a graft polymerization results in a stable copolymer with essentially no added graft monomer on the functionalized vinylamine-containing polymer via Michael addition and provides a polymer of different chemical and physical properties compared with other linear polymers.
All references cited in this application are incorporated herein in their entirety.